1. Field of the Invention
The present invention relates to improvements in a reinforcement used for reinforcing a joint at which two lengths of an optical-fiber cable or optical waveguide are spliced by fusion welding.
2. Discussion of the Prior Art
To improve the reliability of a fusion-welded joint of an optical fiber cable, it is effective to secure both of fusion-spliced stripped parts of optical fibers and coated or covered portions of the cable, to a suitable reinforcement member. Conventionally, such a reinforcement member is usually made of a plastic or metallic material. However, the conventionally used reinforcement member has some problems, such as a thermal stress developed in the optical fibers due to a relatively large difference in coefficient of thermal expansion between the materials of the reinforcement member and the optical fibers, and inability to permit visual inspection of the joint, due to opacity of the reinforcement member. In view of these problems, it has recently been proposed to use a reinforcement member which is made of a transparent crystallized glass having a low coefficient of thermal expansion, as disclosed in laid-open publication No. 58-105505 (published on July 18, 1983) of Japanese Utility Model Application. In this case, the reinforcement member is produced by machining a crystallized glass workpiece to desired dimensions. As is usually the case with ceramic materials in general, the mechanical strength of the crystallized glass material is remarkably reduced if the material cracks on its surfaces during machining thereof. As a result, the reinforcement member produced from such a glass material tends to be easily damaged or broken if dropped or upon application of pressure to secure the optical fibers, during an operation to reinforce the joint of the optical-fiber cable with the reinforcement member. In particular, this insufficiency of mechanical strength of the reinforcement member is a big barrier to improved reliability of the joint of the optical-fiber cable, under a recent increasing need of miniaturizing the reinforcement member while dealing with an increasing number of fibers used in a cable. In an effort to eliminate minute cracks on the surface of the reinforcement member, which causes the deterioration of the mechanical strength, an attempt was made to treat the reinforcement member with a hydrofluoric acid. However, the treatment with the hydrofluoric acid roughened or frosted the entire treated surface, causing the reinforcement member to lose its transparency. Further, the attempt encountered a problem of pollution due to the use of the hydrofluoric acid. For these reasons, the above method was not practiced in the industry. Another disadvantage of the conventional reinforcement member made of a crystallized glass was recognized in the art. Namely, an adhesive agent applied to a joint for securing the optical fibers to the reinforcement member easily loses its adhesiveness to the optical-fiber cable, due to moisture, etc., during use of the optical-fiber cable. Thus, there has been a need in the industry, to provide a solution to the problems discussed above.